<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        *{
            margin: 0px;
            padding: 0px;
        }
        a{
          text-decoration: none;
        }
        ul{
            list-style: none;
        }
        /*以上为必写内容*/
        .nav{
            width: 960px;
            height: 60px;
            background: darkturquoise;
            margin: 0 auto;
        }
        .nav1>li{
            display: inline-block;
            height: 60px;
            line-height: 60px;
            background: white;
            padding: 0 65px;
            float: left;
            color: black;
        }
        .nav10>li{
            display: none;
            height: 15px;
            line-height: 15px;
        }
        .nav1>li:hover>.nav10>li {
            display: block;
        }
       .nav1>li:hover>a{
            color: red;
           text-decoration: underline;
       }
        .nav1>li>a{
            color: black;
        }
        .nav100>li{
            position: relative;
            left: 42px;
            top: -15px;
            display: none;
        }
        .nav10>li:hover>ul>li{
            display: block;
        }
    </style>
</head>
<body>
<div class="nav">
    <ul class="nav1">
        <li><a href="#">首页</a></li>
        <li>
            <a href="#">知识讲堂</a>
            <ul class="nav10">
                <li>英语
                    <ul class="nav100">
                        <li>中国英语</li>
                        <li>英国英语</li>
                    </ul>
                </li>
                <li>语文</li>
                <li>数学</li>
            </ul>
        </li>
        <li>
            <a href="#">在线交流</a>
        </li>
        <li><a href="#">关于我们</a></li>
        <li><a href="#">联系我们</a></li>

    </ul>
</div>
</body>
</html>